The present invention relates to a transfer unit for launching pig balls into a pipeline and for receiving the pig balls from a downstream portion of the pipeline, the launching and receiving transfer units including many common features to facilitate their operation in the cleaning and maintenance of pipelines.
In pipelines for transporting various fluids, either gases or liquids, from one location to another, it is commonly necessary to clean various materials from the interior of the pipeline in order to maintain efficient operation. For example, pipelines carrying gases under pressure are commonly susceptible to collection of liquids produced, for example, by condensation or the like, the liquid tending to collect in relatively low portions of the pipeline. Similarly, pipelines adapted for carrying liquids such as mineral oils are susceptible to a coating of paraffin wax being deposited upon the interior of the pipeline. Such deposits tend to decrease the effective cross-sectional area of the pipeline and thereby restrict or otherwise interfere with flow through the pipeline.
Accordingly, it has become common practice to employ spheres commonly referred to as "pig balls" which are injected or launched into the pipeline and carried by fluid pressure along a portion of the pipeline to be cleaned. The pig balls are selected to have a diameter closely approximating the inside diameter of the pipeline. Accordingly, the pig balls are commonly formed from hollow rubber or elastomer shells which are filled under pressure with a fluid to establish the outside diameter of the pig ball. Thus, the outside diameter of the pig ball may be closely controlled in relation to the inside diameter of the pipeline to insure a tight fit so that, as the pig ball is propelled or moved through the pipeline, its especially formed surface cleans foreign material from the interior of the pipeline. On the other hand, the pig balls may be employed in pipelines adapted for carrying fluids such as gases to remove liquids from relatively low portions of the pipeline.
In any event, it is particularly important to facilitate launching of the pig balls into the pipeline and removal of the pig balls from a downstream portion. Obviously, cleaning operations employing passage of the pig balls through the pipeline interfere with normal transport operations by the pipeline so that efficient launching and retrieval of the pig balls are essential for economical operation of the pipeline.
At the same time, it is important to understand that pig balls of the type contemplated by the present invention may be employed for cleaning pipelines having large inside diameters of greater than six inches or one foot. Commonly, pipelines of the type contemplated by the present invention have an inside diameter in the order of 36 or 48 inches, requiring transfer units for efficiently launching pig balls of a similar size into the pipeline and for retrieving them from a downstream portion thereof.
The transfer units necessarily include valve means for selectively isolating a magazine adapted to contain the pig balls. The magazine may be employed either as a starting point from which to launch the pig balls into the pipeline or as a collecting point in which to receive the pig balls as they emerge from the pipeline. In any event, it is also important to assure proper operation of the transfer units over extended periods of time. It is also important to design the transfer units so that they may be operated and maintained while minimizing interference with normal transport operation of the pipeline.
Accordingly, there has been found to remain a need for a transfer unit capable of efficiently and reliably transferring pig balls into and out of pipelines minimizing interference with normal transport operation of the pipeline and facilitating maintenance of the transfer units themselves.